1. Field of the Invention
This invention relates to a loading device and a shifting device for a disc-shaped recording medium. More particularly, it relates to a loading device for a disc-shaped recording unit having a loading member, and a shifting device for the disc-shaped recording medium.
2. Background of the Invention
There has hitherto been proposed a disc-shaped recording medium, such as an optical disc, a magnetic disc or a magneto-optical disc. Such disc-shaped recording medium is referred to hereinafter as a disc. There has also been proposed a disc recording and/or reproducing apparatus having recording/reproducing means for recording and/or reproducing information signals on or from the disc. Such disc recording and/or reproducing apparatus includes a disc loading device for loading the disc on recording/reproducing means.
The disc loading device described in, for example, JP-B-04 4671, is so arranged and designed that a disc introduced from the front side of the loading device is clamped between a stationary roll and a driving roll kept parallel to each other and is transferred towards the rear side under the driving force of the driving roll.
With such loading device, when the disc transferred by the rolls reaches a region overlying a disc loading portion (disc table) constituting the recording/reproducing unit above a chassis, the disc is first released from a clamped state by the rolls. The disc is then clamped by the disc loading portion and a clamping plate (chuck plate) mounted above the disc loading portion so as to be loaded on the recording/reproducing unit. The clamp plate is rotatably mounted on the foremost part of a clamp member (chuck arm) pivotally mounted at its proximal end.
The operation of shifting the driving roll into and out of contact with the stationary roll and the operation of rotating the clamp plate into and out of contact with the disc loading portion are carried out by shifting loading arms (loading members) mounted laterally of a base member. These loading arms are rotatably supported with respect to a frame and rotated under the driving force exerted by a motor and a plunger driven in dependence upon the disc position.
With the above-described disc loading device, since the loading arms taking charge of the shifting of the driving roll and the rotation of the clamping member are mounted laterally of the base member, it is difficult to reduce the size of the device along the lateral sides. On the other hand, since the loading arms are shifted in a direction along the thickness of a disc recording and/or reproducing apparatus having the disc loading device contained therein, that is, in a direction substantially normal to the major surface of the base member, it is difficult to increase the possible shifting distance of the loading arms. If the shifting distance of the loading arms is small, it is difficult for the driving roll and the clamp member to be shifted over a sufficient distance.
In addition, frequently the base member is supported in a floating manner by means of an elastically deformable vibration-absorbing member. Since the base member can be moved in such a case by the deformation of the vibration-absorbing member, it is necessary for the base member to be held against possible movement when the disc is transferred relative to the base member. It is desirable that the base member be held in this manner in conjunction with the transfer of the disc, that is, with the rotation of the loading arms. However, since the loading arms are mounted laterally of the base member, a link mechanism of a complicated construction needs to be provided for transmitting the rotation of the loading arms to the mechanism holding the base member.
Moreover, with the shifting device constituting the above-described loading device, it is necessary to halt the operation of chucking the disc during transfer of the disc. Apart from the shifting device in the disc loading device, there may be occasions wherein an operation needs to be halted in a stand-by state while another operation proceeds on. Consequently, should the shifting device be designed to be driven by a motor, it is necessary to produce such an operating state in which the chuck operation is halted even when the motor is driven in rotation.
For this reason, it has been customary with the shifting device to halt the transmission of the driving force to a given motion transmitting mechanism by interrupted gear teeth formed in a drive force transmitting follower gear while the driving force is being transmitted to another motion transmitting mechanism.
However, should the transmission of the driving force be halted by the interrupted gear teeth, there is a risk that, if the teeth are not phased correctly to each other at the start of transmission of the driving force, that is, when the driving gear meshes with the first tooth next to the interrupted gear teeth, the gear teeth strike each other to halt the driving gear and the follower gear. While it may be contemplated to lower the height of the first tooth next to the interrupted gear teeth or to design the first gear tooth so as to be elastically deformed for preventing such accident from occurring, problems are raised in connection with operational reliability and durability. Above all, if a larger driving force needs to be transmitted or a larger load needs to be sustained by the follower gear, there is a risk that the teeth would be broken or the follower gear would be unable to mesh with the driving gear.